Porsche is adding a Turbo S to the lineup by squeezing another 50 hp out of its awesome 4.8-liter, twin-turbo V-8. This model is not exactly a surprise: The Panamera’s V-8 engines are shared with the Cayenne, and the last-generation Cayenne was already offered with a 550-hp variation. (Here's a wild prediction: Porsche will add a new Cayenne Turbo S soon.)

The Panamera is a big and heavy car, but it shines as it thunders down the road at surreal speeds. Modified engine management and improved titanium-aluminum turbochargers enable the aforementioned 550 hp, as well as 553 lb-ft of torque, up from 516 for the regular Turbo. In the chassis’s "Sport" and "Sport Plus" modes, an overboost function increases the twist to a wild 590 lb-ft. The regular Turbo can muster an already-impressive 568 lb-ft under overboost, which is accessed by paying for the Sport Chrono package. This package is standard in the Turbo S.

The added power translates into performance you won't need to complain about: Porsche says 60 mph can be achieved in 3.6 seconds, but we clocked the regular Turbo at 3.3. Figure a tenth or two quicker than that, thanks in large part to the seven-speed dual-clutch PDK automatic, which includes a launch-control function. It is the only available transmission. The company claims a top speed of 190 mph, but based on our testing, the real-world figure will be higher by about 5 mph. If you care, Porsche has no final fuel-economy ratings yet, but it says they will be close to the Turbo’s city/highway figures of 15/23 mpg.

No major changes were made to the chassis, which can be considered supremely competent even among high-performance sedans, but the rear track has been engorged by specific 20-inch Turbo II wheels. Europe gets the option of low-rolling-resistance tires on 19-inch wheels, which increase efficiency—yippee!

The slight performance increase comes at a not-so-slight premium. Porsche is asking for a cool $174,175, as opposed to the $136,275 required for a Panamera Turbo. For that money, you get some of the Turbo’s performance options as standard (Porsche Dynamic Chassis Control, Sport Chrono, etc.), as well as side skirts out of the "Porsche Exclusive" parts bin and the choice of special color combinations. Agate gray metallic is exclusive to the Panamera Turbo S, and inside there are two color combos—black/cream and agate gray/cream—that you can't get on any other Panamera. We predict these color choices will prove to be especially popular among Turbo S customers, who will be eager to point out to their friends exactly what they got for an extra $38K. (It’s worth mentioning that Porsche also offers a $21,000 Power Pack to upgrade your Panamera Turbo to 540 hp, but it doesn’t include all the S goodies.)

The spacious Porsche hatchback remains the second-fastest sedan in the VW Group—the Bentley Continental Flying Spur Speed has a top speed of 200 mph—and that’s not likely to change for a while, at least until the Bugatti Galibier comes to market. And, if anything, it will serve as a nice benchmark for Audi and its upcoming RS